A patient with a high degree of with-the-rule astigmatism fitted with a spherical gas permeable lens will show touch?

When fitting a patient with high degrees of with-the-rule astigmatism using a spherical gas permeable lens, it is important to understand how the lens interaction with the cornea manifests. With-the-rule astigmatism refers to a condition where the vertical meridian of the eye has a greater curvature than the horizontal meridian.

In this scenario, a spherical lens will not provide the necessary power to compensate for the astigmatism correctly at both meridians. Since the vertical meridian is steeper, the spherical lens will tend to align more towards the horizontal axis, resulting in slight movement when the eye moves. This causes the lens to touch or exhibit interaction primarily on the horizontal meridian.

Therefore, when observing this type of fit, touch will be noted on the horizontal meridian due to the way the spherical lens affects the corneal curvature, leading to the conclusion that touch is felt on the horizontal meridian. This understanding is critical for practitioners to ensure proper lens fitting and to make necessary adjustments to address the astigmatism correctly.